WASHINGTON — Elizabeth Warren arrived at the Capitol on Thursday morning carrying a black L.L. Bean backpack in the manner of a student in one of her former Harvard classes. Inside was her treasured, tattered King James Bible, used since third grade and chosen for her Senate swearing-in.

“I know people come with big fancy family Bibles,” Warren said in an interview before her induction. “Mine’s a little more modest.”

As she waited, the first woman elected to the Senate from Massachusetts mused about the moment.

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“This chair, this particular Senate seat, was held by John Quincy Adams, Daniel Webster, [Charles] Sumner — and of course Senator [Edward M.] Kennedy for half a century,” Warren said. “Men of principle, men who fought hard for the people of the Commonwealth of Massachusetts and for this country.”

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As Warren and Representative ­Joseph Kennedy III on Thursday became the Capitol’s newest elected officials from Massachusetts, they ushered in a rapidly transforming Massachusetts delegation.

Recent turnover has injected new blood — and additional star power — into the delegation, but the newcomers ­also bring a relative lack of experience, a sharp contrast to the seasoned veterans who until recently defined the delegation and nurtured its considerable influence.

The turnover comes as two longtime stalwarts — John Olver and Barney Frank, 53 years in Washington between them —retired, and Republican Scott Brown is back in Massachusetts after losing to Warren. More change is expected soon, as Senator John F. Kerry prepares for confirmation hearings to become secretary of state and Representative Edward J. Markey
plans to run for his seat (possibly against Brown).

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“Massachusetts has long had some of the most powerful delegations year in and year out,” said Jim Manley, a Democratic strategist and former aide to Senator Kennedy. “I’m afraid that’s something that’s going to change.”

Indeed, the last time Massachusetts lost two members of Congress at the same time was 1997 — when two Republicans, Peter Blute and Peter Torkildsen, both lost reelection bids.

In addition, from 1962 to 2009, Massachusetts had only five people serve as US senator. If Kerry leaves, at least five people will have served as senator since Kennedy’s death in 2009.

With Kerry all but gone, Massachusetts would lose the eighth most senior member in the US Senate. If Markey wins that seat, the state would lose the ninth most senior member in the US House.

In a building where seniority matters in setting an agenda, the Massachusetts delegation could have relatively ­junior members steering the way.

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Within weeks, Warren may be the state’s senior senator, if Kerry is confirmed as secretary of state as expected.

On Thursday, Kerry seemed to relish his role as senior statesman. In the morning he was alongside Warren when she was sworn in, holding her elbow, giving her fist pumps, and leading her around.

In the afternoon, he strolled over to the House chamber and found Kennedy in the hallway as he wrapped up an interview.

Kerry dispensed hugs to Kennedy family members and then asked if he could steal the new congressman for a minute.

Kerry and Kennedy then walked onto the House floor, out of the reach of prying ears. Several minutes later, Kennedy emerged and said that Kerry had imparted “words of wisdom.”

Kennedy was joined on Thursday by several family members, including his new wife, Lauren (whom he met when the two of them were students in Warren’s class at Harvard Law School); his twin brother, Matt, and his wife, Kate; his mother, Sheila; his stepmother, Beth; and his aunts Kerry, Kathleen, and Vicki.

His father, former congressman Joe Kennedy II, joined him on the House floor as he was sworn in. “It’s a thrill. It’s exciting,” Representative Kennedy said. “It’s been a bit of a whirlwind today.”

Massachusetts has long had outsized political clout for its relatively small delegation, with major players on issues like health care, financial regulation, foreign affairs, and global warming. One reason was the legacy of the late House speaker Thomas P. “Tip” O’Neill, who made a point to position Massachusetts lawmakers on key committees in the House. Over time, those members rose to senior roles.

This time around, the newest Kennedy, despite his ­famous name and gold-plated political stock, couldn’t get a slot on his preferred House Education Committee.

“I’ve seen a lot of transition during my career on Capitol Hill — and there’s no question we’re going to feel the loss of Senator Kerry and of Barney and of John Olver,” said Representative James McGovern,a Democrat from Worcester who started as a congressional aide to Representative Joe Moakley.

“We’re like a family,” McGovern added. “You’re used to seeing these people every day and then all the sudden we won’t. On a personal level all of them are going to be missed. In terms of seniority and clout and brain power, that also is going to be missed.”

Warren still doesn’t have a house to live in (she’s going apartment-hunting on Friday). And she has been told she will be in a double-wide trailer until an office can be secured for her, sometime by April.

Because she doesn’t have a proper office yet, Warren sat for an interview in a committee conference room in one of the buildings furthest away from the Senate floor.

Warren declined to say whether she would have voted for the fiscal cliff deal, but she was critical of the negotiation struck by Vice President Joe Biden and Senate minority leader Mitch McConnell.

“I’m just now learning all the details of the deal,” she said. “Giveaways to big corporations at a time when we’re under enormous financial pressure? You know, this whole deal was supposed to be about bringing our house into financial order, not giving more away to some of the biggest corporations in this country.”

Warren also declined to endorse Markey, who is planning to run for Kerry’s seat. Markey, a Malden Democrat, has been endorsed by Kerry, Victoria Reggie Kennedy, and the Democratic Senatorial Campaign Committee.

Warren made history by becoming the first female senator from Massachusetts, and she recounted telling little girls on the campaign trail, “My name is Elizabeth, I’m running for the United States Senate. Because that’s what girls do.”

After being sworn in, she walked over to Senator Barbara Mikulski, a Maryland Democrat and the first woman to be elected to US Senate without assuming her husband’s seat.

Mikulski affixed a US Senate pin to Warren’s lapel, telling her it was “the croix de guerre for all the battles we women have fought.”

Meanwhile, as Warren navigates the halls of Congress, she has newfound empathy for the first-year students she taught in law school.

“It is like the first day of school, over and over. It’s new beginnings,” she said. “I feel the weight of history. But also the urgency of the future.”